1. Field of the Invention
The present invention relates to a spare battery unit which is chargeable so as to supply an electric power to battery-driven machines such as a notebook type personal computer and, more particularly, to an adapter for an external battery and a battery system including such an adapter.
2. Description of the Related Art
Various battery-driven machines which utilize a chargeable battery as their power source have become widespread.
An example of such machines is a notebook type personal computer. A notebook type personal computer is advantageous in that it is portable because it is driven by a battery removably installed in the interior of the machine without the need for connection with the mains power. Before the power of the battery is consumed, the battery is charged by a charger, thereby maintaining the function of the battery.
A conventional battery will now be explained with reference to FIG. 3.
A personal computer 1 is provided therewithin with an internal battery 2 which is removable and chargeable, and the electric power of the battery 2 is utilized for various operations. When the internal battery 2 is charged, a predetermined DC is supplied from a DCIN terminal 3 and introduced to the internal battery 2 so as to charge it.
For this purpose, the DCIN terminal 3 is connected to a DC cable 4, and the DC cable 4 is connected to a plug 6 through an AC adapter/charger 5.
The AC power (usually AC 100 to 240 V) from the plug 6 is converted into a predetermined DC power (e.g., DC 12 V) by the AC adapter/charger, and input to the DCIN terminal 3 of the personal computer 1 through the DC cable 4, thereby charging the internal battery 2.
In this way, by charging the internal battery 2 with a predetermined frequency, it is possible to maintain the power of the internal battery 2 and to drive the personal computer by utilizing the power.
However, since the capacity of the internal battery 2 is limited, the computer can be operated for about 2 hours at most without recharging the internal battery. Although it is possible to prolong the duration of continuous use of the computer by increasing the capacity of the internal battery 2, since the weight of the personal computer 1 is thereby increased, there is a limit to increases in the capacity of the internal battery 2.
In order to permit continuous use of the computer for a long time use without charging while maintaining the light weight of the personal computer 1, a battery identical to the internal battery 2 may be provided as a spare battery which replaces the internal battery 2 after a predetermined time has passed.
However, during the period when the batteries are being changed, the power supply to the personal computer 1 is zero, so that the data and the like which are stored in a RAM or the like of the personal computer 1 are lost. To prevent this, a battery for backing up the RAM is provided in the personal computer 1 separately from the internal battery 2 so as to save the data and the like in a memory such as a magnetic disk which can store the data before the power supply to the personal computer is cut off for the purpose of exchanging the batteries.
This is, however, also disadvantageous in that the system for providing the backup battery within the personal computer 1 requires an additional device, which occupies a considerable space in the personal computer 1, increases the weight of the computer and leads to an increase in cost.
Especially, since the backup battery is not operated for any significant period of time, it is inefficient to provide it within the personal computer 1.
In addition, it is troublesome for the user to save the data and the like in a magnetic disk or the like before exchanging the batteries and to restore the data after they are exchanged.